Error free(): Invalid next size (fast)

Question

I have a very simple program that malloc()'s some data, initializes it, then frees it and I keep getting this error. I have no idea why this is happening, any ideas?

   #include <stdlib.h>
#include <stdio.h>

int main(){
    int * big_mem;
    int row_size = 4096; //not sure about this....
    int num_rows = 5;
    int const_val = 0xFFFFFFFF;

    big_mem = (int *) malloc(row_size * num_rows);
    if(!big_mem){
        printf("Failed to malloc, exiting...");
        return 0;
    }

    i = 0;  
    for(; i < row_size * num_rows; ++i){
        big_mem[i] = const_val;
    }
    printf("Initialized mem, ");

    free(big_mem);
    big_mem = NULL;

    return 0;
}

Output:

*** Error in `./test': free(): invalid next size (fast): 0x0000000000819010 ***

Answer 1

Use malloc(row_size * num_rows * sizeof(int)) .

You didn't malloc enough memory so your loop wrote past your malloc()ed memory. I'm surprised you didn't just get a segmentation fault.